It is well known that diesel engines provided with prechambers have lower hydrocarbon and oxides of nitrogen emission levels than direct injection engines. In prechambered engines, high levels of turbulence in the prechamber and in the main combustion chamber cause excellent mixing of fuel droplets and unconsumed oxygen resulting in low hydrocarbon emissions. At the same time, oxides of nitrogen emissions are low in prechambered diesel engines as well. Typically, within the engine prechamber, there is a greater amount of fuel than that required for stoichiometric combustion which tends to cool the mixture within the prechamber so that combustion at high temperatures conducive to the formation of, for example, nitrous oxide, are avoided. And, as the burning mixture exits the prechamber, it is immediately diluted by the relatively cool compressed air in the main combustion chamber. Consequently, high temperatures do not exist in either the main or prechamber, which high temperatures would tend to cause the formation of oxides of nitrogen.
Conversely, a prechambered diesel engine has a higher surface to volume ratio than a direct injection engine and, when liquid cooled, there is a commensurate increase in heat rejection to the liquid coolant. Moreover, because of the greater turbulence in the combustion volume in a prechambered engine, the heat transfer coefficient is increased which results in additional heat rejection over and above that which would occur in a direct injection engine.
As a consequence, to dissipate the large amount of heat rejected to the liquid coolant, relatively larger radiators are required for prechambered engines than for direct injection engines. This of course contributes to the cost of the engine.
Moreover, because prechambers in liquid cooled diesels are also liquid cooled, they do not warm up to operating temperature as rapidly as might be desired making start-up difficult and prolonging the time of warm-up.
Prior art depicting the foregoing structure and/or of possible relevance to the invention hereinafter described and claimed include the following, all U.S. Pat. Nos.: 2,406,446 issued Aug. 27, 1946 to Ware; 2,866,445 issued Dec. 30, 1958 to Graves; 2,985,155 issued May 23, 1961 to Hockel; 3,105,470 issued Oct. 1, 1963 to Hockel et al; and 3,168,079 issued Feb. 2, 1965 to Henderson.